1. Field of the Invention
The present invention relates to a battery remaining detection method for detecting the remaining capacity of a battery, such as a lithium-ion secondary battery.
2. Description of the Related Art
The remaining capacity of a secondary battery, such as a lithium-ion secondary battery, has hitherto been estimated from the terminal voltage of the battery. That is, as a method of detecting the remaining capacity of a secondary battery, a voltage method has been proposed. This voltage method is a method of measuring the voltage of a secondary battery and computing the capacity of the secondary battery on the basis of the correlation between the voltage and the capacity of the secondary battery.
In a secondary battery, such as a lithium-ion secondary battery, when the capacity is estimated using the voltage method, the remaining voltage is estimated from the terminal voltage of the secondary battery by using the voltage-capacity correlation table of the lithium-ion secondary battery. A voltage drop is computed on the basis of the current and the internal resistance of the secondary battery, and conversion into the capacity is performed.
In the above-described voltage method, however, as a typical problem, an accurate capacity cannot be obtained at a change point of current, for example, a discharge start point or a charging start point. This is because there is a polarization voltage due to the polarization characteristics of the secondary battery. When discharge current begins to flow, a large capacity of the secondary battery appears because of the influence of the polarization voltage, and there is a difference in voltage drop between the time immediately after (at the time discharge starts) the current is changed and a time after some time has elapsed (e.g., 10 minutes). Therefore, if the capacity of the secondary battery is estimated on the basis of the voltage-capacity correlation table of the secondary battery by ignoring the polarization characteristics of the secondary battery, the error of the capacity appears to be large when the current is changed.